[Cryptography] Finding Nemo's random seed

[John Denker]

On 09/05/2017 01:22 AM, iang wrote in part:

> no way to retrieve the original seed value for that generator. So
> animators manually replicated the plants’ movements frame by frame, a
> laborious process. The fact that the studio had lost access to its
> own film after less than a decade is a sobering commentary on the
> challenges of archiving computer-generated work.

This has been understood in the physics community since the
1940s.

The root cause is ambiguity in the concept of "randomness" itself.
The type of "randomness" you want depends greatly on the application:
 -- Sometimes you want something that is entirely deterministic and
  predictable, just complicated-looking, e.g. sea grass.
 -- Sometimes you want to guarantee that Thing A is uncorrelated with
  Thing B.  Randomization is one way of doing this, but not the only
  way or even the best way.  Applications include spread-spectrum
  communication codewords, radar pulses, Monte Carlo integration,
  et cetera.
 -- Sometimes you want cryptographically-strong completely-unpredictable
  randomness.